Percutaneous transluminal coronary angioplasty (PTCA) is a procedure by which a balloon dilatation catheter is inserted into and manipulated within a patient's coronary arteries to unblock an obstruction (a stenosis) in the artery. Typically, the catheter is about 150 cm long and is inserted percutaneously into the patient's femoral artery in the region of the groin. The catheter then is advanced upwardly through the patient's arteries to the heart where, with the aid of a guidewire, the catheter is guided into the coronary artery where it can be controlled to perform the angioplasty procedure, described below.
In one type of balloon dilatation catheter, the catheter has two lumens. One lumen, for inflation and deflation of the balloon, extends from a fitting at the proximal end of the catheter and opens distally into the interior of the balloon. The balloon is inflated with a liquid and is deflated by aspirating the liquid from the balloon through the inflation/deflation lumen. The second lumen extends from another fitting at the proximal end of the catheter through the catheter and is open at the distal tip of the catheter shaft. The second lumen is adapted to receive a guidewire, such as a steerable small diameter guidewire. The first and second lumens may be arranged either in a parallel arrangement, in which the lumens are disposed side-by-side, or may be arranged in a coaxial manner in which one lumen is of a lesser diameter and is disposed within the other, larger diameter, lumen.
In a conventional coaxial PTCA balloon dilatation catheter, the elongate catheter shaft is formed from an inner tube and a coaxial outer tube. The inner tube extends from the proximal end fully to the distal end of the catheter and terminates in an open distal outlet. The lumen extending through the inner tube serves as a guidewire lumen. The outer tube extends from the proximal end of the catheter and terminates short of the distal end of the inner tube. The dilatation balloon is mounted on the distal end of the catheter with its proximal end adhesively attached to the distal end of the outer tube and the distal end of the balloon being adhesively attached to the distal end of the inner tube. The annular lumen defined between the inner tube and the outer tube communicates with the interior of the balloon and serves as the inflation/deflation lumen.
In a typical procedure, the guidewire is preliminarily loaded into the catheter and the assembly is inserted into a previously percutaneously placed guide catheter that extends to the region of the patient's heart and terminates at the entrance to the coronary arteries. The assembly of the balloon angioplasty catheter and the steerable guidewire is advanced through the guide catheter to the entrance to the coronary arteries. The guidewire then is projected into the coronary arteries and is steered by manipulation from its proximal end, while being observed under a fluoroscope, until the guidewire passes through the stenosis in the artery. Once the guidewire is in place, the balloon dilatation catheter is advanced over the guidewire, being guided directly to the stenosis to place the balloon within the region of the stenosis. Once in place, the balloon is inflated under substantial pressure to dilate the stenosis.
The anatomy of human vasculature, including the coronary arteries, varies widely from patient to patient. Often a patients coronary arteries are irregularly shaped and highly tortuous. The tortuous configuration of the arteries may present difficulties to the physician in properly placing the guidewire and then advancing the catheter over the guidewire. A highly tortuous coronary anatomy typically will present considerable resistance to advancement of the catheter over the guidewire. With certain types of catheter construction, the increased resistance may tend to cause portions of the catheter to collapse or buckle axially. For example, in a catheter having a shaft formed from inner and outer coaxial tubes, the balloon is mounted to the distal ends of the tubes. There may be a tendency for the tubes to telescope axially when presented with an increased resistance. The telescoping of the tubes will tend to draw the ends of the balloon together slightly but sufficiently to cause the balloon to become bunched up as it is forced through the stenosis because the length of the balloon will become shorter than when the coaxial tubes are in their normal, non-telescoped position. The bunching up of the balloon makes it more difficult for the balloon to be pushed into the stenosis.
The problems associated with the telescoping of the inner and outer tubes and the bunching of the balloon have been addressed by providing an anchor joint for to anchoring the distal end of the outer tube to the inner tube at a location in the distal region of the catheter. By preventing the telescoping of the inner and outer tubes, the length of the balloon does not contract, and bunching of the balloon is avoided. Such an anchor joint is illustrated in FIG. 1, taken from U.S. Pat. No. 5,759,191 shown in FIG. 1, the catheter is of coaxial construction with a annular space 20 forming the inflation lumen for the catheter. Inflation fluid annular space 20 through holes or other suitable openings 22 formed in the outer tube 12 to inflate the balloon.
The inner tube 10 has a guidewire lumen 24 to receive a guidewire used in a conventional manner. In FIG. 1, an inner tube 10 is shown as anchored to the outer tube 12 at an anchor joint 16 at the distal end 14 of the outer tube. The joint may be in the form of a ring-like spacer. The ring-like spacer 16 may be replaced by other means to join the outer and inner tubes, such as a weld or a tapering of the diameter of the tube 12 in the region of its distal end to a diameter about the diameter of the inner tube. Gluing or other well known means to join the distal end 14 of the outer tube to the inner tube 10 may be used to secure the tapered portion of the outer tube to the inner tube. By anchoring of the inner tube 10 to the outer tube 12, the balloon 18, when encountering a stenosis or other blockage within the arterial system of the patient, will resist bunching up and will substantially maintain its full length.
The catheter described in U.S. Pat. No. 5,759,191 improved on the prior art by anchoring the distal end of the outer tube to the inner tube. This arrangement increases the column strength and resists axial buckling of the catheter. The relative axial movement and telescopic buckling of the inner tube within the outer tube is avoided when the distal end of the catheter meets substantial resistance to advancement, as when crossing a difficult stenosis or negotiating tightly curved coronary arteries. Because the outer and inner tubes are affixed to one another, the inner tube cannot move, relative to the outer tube, either in a distal or a proximal direction.
It has been discovered that with some catheters, anchoring of the distal end of the outer tube to the inner tube may produce an undesirable side effect. In particular, this may occur with those coaxial balloon dilatation catheters that have balloons formed from a material that stretches more than conventional polyethylene terephthalate (PET). Such compliant balloons will tend to stretch somewhat more in both radial and longitudinal directions when inflated, particularly at higher inflation pressure of the order of 8 atmospheres and above. The longitudinal stretching of the balloon imposes a tension load on that portion of the inner tube that extends between the anchor joint and the distal connection of the balloon at the distal tip of the inner tube. Because the balloon typically will be formed from a material that is more elastic than that from which the inner tube is formed, the distal tip segment of the inner tube may be stretched beyond its elastic limit when the compliant balloon is inflated. Consequently, when the balloon is deflated and returns elastically toward its smaller dimensions, the tip segment of the inner tube may remain in its stretched configuration. Thus, when the balloon contracts toward its original dimensions it will apply a compressive load on the tip segment and may cause the tip segment to bend as suggested in FIG. 2.
As shown in FIG. 2, the inner tube 10 is bent within the balloon 18, and is shown as being distorted over length 24. This distortion of the length 24 can cause additional friction due to the band, for a guidewire moving within the distal portion of the inner tube 10 and this could hinder performance. The distortion of the portion 24 can be so great as to cause the portion 24 of the inner tube to lie against the inner wall of the balloon and affect the shape of the collapsed balloon.